Sulfate contamination in ground water has increased in recent decades due to various human activities. Effluent water from mines release huge amounts of sulfate to the environment, making the water unsuitable for discharge into the environment or for human use. Also, the lowering of ground water tables due to agricultural use causes oxygen to invade the anoxic layer, oxidizing the iron sulfides to Fe(III) hydroxides and generating sulfate. This leaches to the ground water leading to an increase in sulfate concentration. Sulfate also leaches into water supplies from sources like decaying plants and animals; and from chemicals used in the agricultural, textile, and manufacturing industries.
Sulfate contamination of ground water causes many human health hazards. Consumption of water with more than 500 mg/L of sulfate causes a laxative effect, leading to intestinal discomfort, diarrhea, and eventually leading to dehydration. Also, the presence of sulfate salts in the range of 250 to 1000 mg/L imparts unpleasant taste to the water. It has also been reported that sulfate pollution can lead to eutrophication of surface water and increase the corrosive property of the water.
Methods of reducing sulfate contamination include demineralization by reverse osmosis, distillation, or precipitation using chemicals like barium. However, demineralization is prohibitively expensive for use on an industrial scale. Also, while chemical reduction of sulfate using barium chloride also ensures substantial reduction of heavy metals, the extremely high levels of barium chloride necessary for effective remediation of sulfates renders the method unfeasible on an industrial scale.
Bioremediation is an alternative treatment option for reducing sulfate concentrations in ground water. However, treatment of soluble sulfate from waste water using sulfate reducing bacterial (SRB) consortia has limits. For example, a continuous supply of SRB must be maintained, and the bacteria require a continuous supply of a substrate/electron donor to support the reduction of sulfates. While lactic acid is a highly effective substrate for SRB, there is a significant cost associated with running a reactor using commercially available lactic acid.